Variable valve mechanism

ABSTRACT

A first arm member and a second arm member are provided. The first arm member is positioned between a cam and a valve body to oscillate in synchronism with the rotation of the cam. The second arm member changes the angle of the first arm member in accordance with the rotation angle of a control shaft. The temperature prevailing in the neighborhood of the control shaft and cam is detected. The rotation angle of the control shaft is corrected so as to avoid the influence of the detected temperature.

TECHNICAL FIELD

The present invention relates to a variable valve mechanism, and moreparticularly to an internal combustion engine's variable valve mechanismthat is capable of changing the operating angle and lift amount of avalve that opens in synchronism with camshaft rotation.

BACKGROUND ART

A conventional variable valve mechanism disclosed, for instance, byJapanese Patent Laid-Open No. 63023/1995 changes the lift amount of avalve body in an internal combustion engine that is equipped with thevalve body, which opens/closes in synchronism with camshaft rotation.This variable valve mechanism is provided with a swinging arm that ispositioned between a cam and valve body to swing in synchronism with acam operation. The swinging arm is built in the internal combustionengine in such a manner that its basic relative angle in relation to thevalve body is variable. Further, the mechanism includes a lost motionspring and adjustment mechanism. The lost motion spring controls themotion of the swinging arm by directing the swinging arm toward the cam.The adjustment mechanism changes the relative angle of the swinging armto the valve body in accordance with control shaft rotation.

In the variable valve mechanism described above, the lost motion springworks so that the cam is in constant mechanical contact with theswinging arm. Therefore, the variable valve mechanism can constantlytransmit the mechanical force generated by the cam to the valve bodywithout any loss. Further, the variable valve mechanism can change thereference relative angle of the swinging arm to the valve body byrotating the control shaft. When the relative angle changes, the time(crank angle) required for the swinging arm to start depressing thevalve body can be changed after the cam's pushing pressure begins to betransmitted to the swinging arm, that is, after the swinging arm beginsswinging due to cam action.

When the time required for the swinging arm to start depressing thevalve body changes, the crank angle width (hereinafter referred to asthe “operating angle”) for placing the valve body in a non-closed statechanges so that the profile of the lift amount for the valve bodychanges. Therefore, the conventional mechanism described above canchange the operating angle and lift amount or the valve body with a highdegree of freedom.

Including the above-mentioned document, the applicant is aware of thefollowing documents as a related art of the present invention.

[Patent Document 1] Japanese Patent Laid-Open No. 63023/1995

[Patent Document 2] Japanese Patent Laid-Open No. 293216/1995

DISCLOSURE OF INVENTION

However, the ambient temperature of the variable valve mechanism greatlychanges in accordance, for instance, with the operating status of aninternal combustion engine. In the aforementioned conventionalmechanism, therefore, the sections around the control shaft and camshaftare frequently subject to significant expansion or shrinkage due to atemperature change. Such thermal deformation changes the status of theswinging arm, which is positioned between the control shaft and cam, andthe status of the adjustment mechanism, which changes the angle of theswinging arm.

More specifically, when the ambient temperature of the aboveconventional mechanism increases, thermal deformation occurs so as toincrease the spacing interval between the control shaft and camshaft. Asa result, the status of the swinging arm changes in the direction ofproviding a smaller lift. On the contrary, if the ambient temperature ofthe variable valve mechanism decreases, the spacing interval between thecontrol shaft and camshaft decreases so that the status of the swingingarm changes in the direction of providing a greater lift. Therefore, theabove-mentioned variable valve mechanism is at a disadvantage in thatthe valve body's operating angle and lift amount change due to theinfluence of a temperature change in the neighborhood of the valve bodyno matter what the status of the control shaft is.

The present invention has been made to solve the above problems. It isan object of the present invention to provide a variable valve mechanismthat is capable of constantly providing the valve body with a desiredvalve-opening characteristic without being affected by a temperaturechange.

The above object is achieved by a variable valve mechanism according toa first aspect of the present invention. The variable valve mechanism iscapable of changing the operating angle and/or lift amount of a valvebody of an internal combustion engine. The variable valve mechanism mayinclude a control shaft whose status is controlled so as to change theoperating angle and/or lift amount. The mechanism may also include aswinging arm that is positioned between a cam and a valve body to swingin synchronism with cam rotation, thereby transmitting the force of thecam to the valve body. The mechanism may further include an adjustmentmechanism for changing the basic relative angle of the swinging arm inrelation to the valve body in accordance with the status of the controlshaft. A temperature detection unit may be provided for detecting orestimating the ambient temperature of the control shaft and the cam. Atemperature correction unit may also be provided for correcting thestatus of the control shaft in accordance with the temperature and inorder to avoid the influence of the temperature.

In a second aspect of the present invention, the variable valvemechanism according to the first aspect of the present invention mayfurther include a sensor for detecting the status of the control shaft.The mechanism may also include an actuator for driving the controlshaft. The mechanism may further include an actuator control unit forcontrolling a control value of the actuator in accordance with theoutput of the sensor. The temperature correction unit may correct thecontrol value of the actuator in accordance with the temperature.

In a third aspect of the present invention, the temperature correctionunit in the second aspect of the present invention may correct theoutput of the sensor in accordance with the temperature. The actuatorcontrol unit may controls the control value of the actuator inaccordance with the corrected sensor output.

In a fourth aspect of the present invention, the variable valvemechanism according to the first aspect of the present invention mayfurther include a sensor for detecting the status of the control shaft.An actuator may be provided for driving the control shaft. A targetstatus setup unit may be provided for setting the target status of thecontrol shaft. An actuator control unit may be provided for controllingthe actuator so that the output. of the sensor matches the target statusof the control shaft. The temperature correction unit may correct thetarget status of the control shaft in accordance with the temperature.

The above object is achieved by a variable valve mechanism according toa fifty aspect of the present invention. The variable valve mechanism iscapable of changing the operating angle and/or lift amount of a valvebody of an internal combustion engine. The variable valve mechanism mayinclude a control shaft whose status is controlled so as to change theoperating angle and/or lift amount. The mechanism may also include aswinging arm that is positioned between a cam and a valve body tooscillate in synchronism with cam rotation, thereby transmitting theforce of the cam to the valve body. The mechanism further includes anadjustment mechanism for changing the basic relative angle of theswinging arm in relation to the valve body in accordance with the statusof the control shaft. A member for determining the distance between thecontrol shaft and a camshaft and a member positioned between the controlshaft and the cam are made of materials having the same linear expansioncoefficient.

In a sixth aspect of the present invention, the temperature correctionunit of the first aspect of the present invention may include a statusdetection sensor for detecting the status of the control shaft. Thetemperature correction unit may also include a stop state temperatureacquisition unit for acquiring the ambient temperature at the time of aninternal combustion engine stop as a stop state temperature. Thetemperature correction unit may further include a stop statecharacteristic value detection unit for detecting the operating angleand/or the lift amount at the time of an internal combustion engine stopas a stop state characteristic value in accordance with the status ofthe control shaft. A non-corrective restart state characteristic valuecalculation unit may be provided for calculating a non-correctiverestart state characteristic value in accordance with the stop statecharacteristic value and the difference between an assumed restarttemperature of the internal combustion engine and the stop statetemperature. A correction value calculation unit may be also providedfor calculating a correction value for converting the non-correctiverestart state characteristic value into an operating angle and/or liftamount suitable for the assumed restart temperature. A pre-startupcorrection unit may be further provided for correcting the status of thecontrol shaft prior to an internal combustion engine restart so that theoperating angle and/or lift amount change in accordance with thecorrection value.

In a seventh aspect of the present invention, the pre-startup correctionunit of the sixth aspect of the present invention may correct the statusof the control shaft at time of an internal combustion engine stop sothat the operating angle and/or lift amount change in accordance withthe correction value.

In an eighth aspect of the present invention, the assumed restarttemperature of the sixth or seventh aspect of the present invention maybe the lowest temperature within an operating temperature range of theinternal combustion engine.

In a ninth aspect of the present invention, the temperature correctionunit of the first aspect of the present invention may include a statusdetection sensor for detecting the status of the control shaft. Thetemperature correction unit may also include a stop state temperatureacquisition unit for acquiring the ambient temperature at the time of aninternal combustion engine stop as a stop state temperature. Thetemperature correction unit may further include a stop statecharacteristic value detection unit for detecting the operating angleand/or the lift amount at the time of an internal combustion engine stopas a stop state characteristic value in accordance with the status ofthe control shaft. A stop period temperature acquisition unit may beprovided for acquiring the ambient temperature during an internalcombustion engine stop as a stop period temperature. A stop periodcorrection unit may be also provided for correcting the status of thecontrol shaft during an internal combustion engine stop so that theoperating angle and/or lift amount are maintained suitable for a restartin accordance with the stop state temperature, the stop statecharacteristic value, and the stop period temperature.

In a tenth aspect of the present invention, the stop period correctionunit of the ninth aspect of the present invention may further include afirst characteristic value change amount calculation unit forcalculating a first characteristic value change amount in accordancewith the stop state temperature and the stop period temperature. Thestop period correction unit may also includes a first actualcharacteristic value calculation unit for calculating the sum of thestop state characteristic value and the first characteristic valuechange amount as an actual characteristic value. The stop periodcorrection unit may further include a suitability judgment unit forjudging whether the calculated actual characteristic value is suitablefor a restart. A control shaft correction unit may be provided forcorrecting the status of the control shaft so that the actualcharacteristic value is suitable for a restart when the actualcharacteristic value is judged to be unsuitable for a restart. Apost-correction characteristic value calculation unit may be providedfor calculating a post-correction characteristic value that is obtainedby correcting the control shaft. A second characteristic value changeamount calculation unit may be also provided for calculating a secondcharacteristic value change amount in accordance with a change in thestop period temperature that is caused after the control shaft iscorrected. A second actual, characteristic value calculation unit may befurther provided for calculating the sum of the post-correctioncharacteristic value and the second characteristic value change amountas an actual characteristic value.

In an eleventh aspect of the present invention, the temperaturecorrection unit of the first aspect of the present invention may includea status detection sensor for detecting the status of the control shaft.The temperature correction unit may also include a stop statetemperature acquisition unit for acquiring the ambient temperature atthe time of an internal combustion engine stop as a stop statetemperature. The temperature correction unit may further include a stopstate characteristic value detection unit for detecting the operatingangle and/or the lift amount at the time of an internal combustionengine stop as a stop state characteristic value in accordance with thestatus of the control shaft. A restart request state temperatureacquisition unit may be provided. for acquiring the ambient temperatureupon a request for an internal combustion engine restart as a restartrequest state temperature. A non-corrective restart request statecharacteristic value calculation unit may be provided for calculating anon-corrective restart request state characteristic value in accordancewith the stop state characteristic value and the difference between therestart request state temperature and the stop state temperature. Acorrection value calculation unit may be also provided for calculating acorrection value for converting the non-corrective restart request statecharacteristic value into a characteristic value suitable for a restart.A pre-restart correction unit may be further provided for correcting thestatus of the control shaft prior to an internal combustion enginerestart so that the operating angle and/or lift amount change inaccordance with the correction value.

In a twelfth aspect of the present invention, the internal combustionengine of any one of the ninth through eleventh aspect of the presentinvention may be capable of automatically stopping and starting withoutrequiring an operator intervention.

According to a first aspect of the present invention, the status of theadjustment mechanism and swinging arm, which are positioned between thecontrol shaft and cam, can be changed by rotating the control shaft forthe purpose of changing the valve opening characteristic of the valvebody. The present invention makes it possible to correct the status ofthe control shaft in accordance with the temperature prevailing in theneighborhood of the control shaft and cam, thereby avoiding theinfluence of a change in that temperature. As a result, the presentinvention can constantly provide the valve body with a desired valveopening characteristic without being affected by a temperature change.

According to a second aspect of the present invention, the control shaftcan be placed in a desired state by detecting the control shaft statuswith a sensor and controlling an actuator's control value in accordancewith the output of the sensor. In this instance, the present inventioncan avoid the influence of a temperature change by correcting theactuator control valve in accordance with the temperature.

According to a third aspect of the present invention, the sensor outputfor detecting the control shaft status can be corrected in accordancewith the temperature prevailing in the neighborhood of the control shaftand cam. Therefore, the present invention makes it possible to obtain asensor output in which the influence of the temperature is reflected.The influence of a temperature change can be avoided by controlling theactuator control value in accordance with the corrected sensor output.

According to a fourth aspect of the present invention, the control shaftcan be placed in a desired state by detecting the control shaft statuswith a sensor and controlling the actuator in accordance with the outputof the sensor. In this instance, the present invention can accuratelyavoid the influence of a temperature change by correcting the targetcontrol shaft state to be attained.

According to a fifth aspect of the present invention, the status of theadjustment mechanism and swinging arm, which are positioned between thecontrol shaft and cam, can be changed by rotating the control shaft forthe purpose of changing the valve opening characteristic of the valvebody. Since the member for determining the distance between the controlshaft and camshaft and the member positioned between the control shaftand cam are made of materials having the same linear expansioncoefficient, the present invention can prevent the swinging arm statusfrom being changed by a temperature change. As a result, the presentinvention can constantly provide the valve body with a desired valveopening characteristic without being affected by a temperature change.

According to a sixth aspect of the present invention, the status of theadjustment mechanism and swinging arm, which are positioned between thecontrol shaft and cam, can be changed by rotating the control shaft forthe purpose of changing the valve opening characteristic of the valvebody. The present invention makes it possible to calculate the operatingangle and/or lift amount that are generated when the internal combustionengine restarts with the control shaft status left uncorrected(non-corrective restart state characteristic value), in accordance withthe difference between the temperature prevailing during an internalcombustion engine stop (stop state temperature) and the assumed restarttemperature of the internal combustion engine and with the operatingangle and/or lift amount prevailing during an internal combustion enginestop (stop state characteristic value), and calculate a correction valuefor converting the non-corrective restart state characteristic valueinto a characteristic value suitable for the assumed restarttemperature. Since a correction is subsequently made in accordance withthe correction value prior to an internal combustion engine restart, thevalve body can be constantly provided with an optimum valve openingcharacteristic at the assumed temperature when the internal combustionengine restarts.

According to a seventh aspect of the present invention, the correctionfor acquiring an optimum valve opening characteristic at the assumedtemperature can be made during an internal combustion engine stop.Therefore, the present invention makes it possible to restart theinternal combustion engine immediately after a restart request isgenerated.

According to an eighth aspect of the present invention, the valve bodycan be provided at internal combustion engine startup with an optimumvalve opening characteristic that prevails at the lowest temperaturewithin the operating temperature range. Therefore, the. presentinvention makes it possible to properly start up the internal combustionengine within the entire operating temperature range.

According to a ninth aspect of the present invention, the status of theadjustment mechanism and swinging arm, which are positioned between thecontrol shaft and cam, can be changed by rotating the control shaft forthe purpose of changing the valve body's valve opening characteristic.The present invention can maintain an appropriate operating angle and/orlift amount for a restart during an internal combustion engine stop bycontrolling the control shaft status in accordance with the temperatureprevailing upon an internal combustion engine stop (stop statetemperature), the temperature prevailing during an internal combustionengine stop (stop period temperature), and the operating. angle and/orlift amount prevailing upon an internal combustion engine stop (stopstate characteristic value). As a result, the present invention canalways provide the valve body with an optimum valve openingcharacteristic at an internal combustion engine restart.

According to a tenth aspect of the present invention, the amount of anoperating angle change and/or lift amount change from the stop statecharacteristic value (first characteristic value change amount) can becalculated in accordance with the difference between the stop statetemperature and stop period temperature. Further, the actual operatingangle and/or actual lift amount can be calculated by adding thecalculated change amount to the stop state characteristic value. If thecalculated actual operating angle and/or actual lift amount are notsuitable for a restart, the control shaft status can be corrected sothat the actual operating angle and/or actual lift amount are suitablefor a restart. Subsequently, the actual operating angle and/or actuallift amount are recalculated by determining the sum of the operatingangle or lift amount corrected above (post-correction characteristicvalue) and the amount of an operating angle change and/or lift amountchange caused by a temperature change after the correction (secondcharacteristic value change amount). The control shaft is then correctedeach time the calculation results deviate from values suitable forstartup. As a result, the actual operating angle and/or actual liftamount are maintained suitable for a restart.

According to an eleventh aspect of the present invention, the status ofthe adjustment mechanism and swinging arm, which are positioned betweenthe control shaft and cam, can be changed by rotating the control shaftfor the purpose of changing the valve body's valve openingcharacteristic. When a request for an internal combustion engine restartis generated, the present invention can calculate an operating angleand/or lift amount that are generated when the internal combustionengine is restarted during the status prevailing during the stop state(non-corrective restart request state characteristic value), inaccordance with the difference between the temperature prevailing uponan internal combustion engine stop (stop state temperature) and thetemperature prevailing upon receipt of the request (restart requeststate temperature) and with an operating angle and/or lift amountprevailing upon an internal combustion engine stop (stop statecharacteristic value), and continue to calculate a correction value forconverting the non-corrective restart request state characteristic valueinto a value suitable for a restart. Subsequently, a correction is madein accordance with the correction value prior to an internal combustionengine restart so that the valve body is constantly provided with anoptimum valve opening characteristic for a restart.

According to a twelfth aspect of the present invention, an internalcombustion engine having an automatic stop function and automaticstartup function can constantly provide the valve body with an optimumvalve opening characteristic at a restart. In an internal combustionengine having the above functions, the startup and stop sequences arerepeated. Therefore, when the startability is improved by the presentinvention, the condition of the internal combustion engine can beremarkably improved.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B illustrate the overall configuration of a variable valvemechanism according to a first embodiment of the present invention;

FIG. 2 is a perspective view illustrating a variable valve mechanismthat is provided for one cylinder in accordance with the firstembodiment of the present invention;

FIG. 3 is an exploded perspective view illustrating a first arm memberand a second arm member, which are the components of the variable valvemechanism shown in FIG. 2;

FIGS. 4A and 4B show that the variable valve mechanism according to thefirst embodiment of the present invention performs a small liftoperation;

FIGS. 5A and 5B show that the variable valve mechanism according to thefirst embodiment of the present invention performs a great liftoperation;

FIG. 6 illustrates the actual operating angle-temperature relationshipthat arises in the variable valve mechanism according to the firstembodiment of the present invention;

FIG. 7 is a flowchart illustrating a routine that is executed inaccordance with the first embodiment of the present invention;

FIG. 8 is a characteristic diagram illustrating the operation of thevariable valve mechanism according to a third embodiment of the presentinvention;

FIG. 9 is a flowchart illustrating a routine that is executed in thevariable valve mechanism accordance with the third embodiment of thepresent invention;

FIG. 10 is a characteristic diagram illustrating a typical modifiedoperation of the variable valve mechanism according to the thirdembodiment of the present invention;

FIG. 11 is a characteristic diagram illustrating the operation of thevariable valve mechanism according to a fourth embodiment of the presentinvention;

FIG. 12 is a flowchart illustrating a routine that is executed inaccordance with the fourth embodiment of the present invention;

FIG. 13 is a characteristic diagram illustrating a typical modifiedoperation of the variable valve mechanism according to the fourthembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

[Overall Configuration of the Variable Valve Mechanism]

FIGS. 1A and 1B illustrate the overall configuration of a variable valvemechanism according to a first embodiment of the present invention. Morespecifically, FIG. 1A is a plan view illustrating the entire variablevalve mechanism, and FIG. 1B is a side view that represents view B ofFIG. 1A.

The configuration shown in FIGS. 1A and 1B contains a cylinder head 10of an internal combustion engine. The cylinder head 10 has a pluralityof control shaft bearings 11, which are positioned on both sides of eachcylinder. The control shaft bearings 11 retain a control shaft 12 insuch a manner that the control shaft 12 can rotate. The internalcombustion engine according to the present embodiment has four cylindersthat are arranged in series. The control shaft 12 is positioned to runlongitudinally over the four cylinders.

Each cylinder of the internal combustion engine has an intake valve andan exhaust valve, which open/close in synchronism with cam rotation(these valves are not shown in FIG. 1A or 1B). The variable valvemechanism according to the present embodiment is a mechanism forallowing at least the intake valve of each cylinder to change itsoperating angle and lift amount. The above-mentioned control shaft 12 isa component whose rotation position is controlled to permit operatingangle and lift amount changes.

When the intake valve operating angle and lift amount can be freelychanged, it is possible to control the intake air amount by controllingthe intake valve operating angle and lift amount without using athrottle valve. When the intake air amount is controlled in such amanner, it is possible to prevent the intake pipe pressure from beingnegative, thereby avoiding a pumping loss within the internal combustionengine. It is assumed that the internal combustion engine according tothe present embodiment is of a throttle-less type, which provides theabove advantage by controlling the intake air amount with the variablevalve mechanism without using a throttle valve. The variable valvemechanism will be described in detail later with reference to FIGS. 2,3, 4A, 4B, 5A, and 5B.

A first gear 14, which is a spur gear, is fastened to an end of thecontrol shaft 12. The first gear 14 meshes with a second gear 16, whichis also a spur gear. A rotation shaft 18 is fastened to the center ofthe second gear 16. As shown in FIG. 1B, a semicircular worm wheel 20 isfastened to the rotation shaft 18 and superposed over the second gear16. The worm wheel 20 meshes with a worm gear 24, which is fastened tothe rotation shaft of a motor 22. When the configuration described aboveis employed, the rotation position of the control shaft 12 can becontrolled by controlling the rotation of the motor 22.

A rotation angle sensor 26 is also mounted on the end of the controlshaft 12 in order to detect the rotation position of the control shaft12. The output of the rotation angle sensor 26 is supplied to an ECU(Electronic Control Unit) 28. A water temperature sensor 29 iselectrically connected to the ECU 28 in order to detect the coolingwater temperature THW of the internal combustion engine. The ECU 28 candetect the outputs of the rotation angle sensor 26 and water temperaturesensor 29, and control the status of the motor 22.

The relationship between the output of the rotation angle sensor 26 andthe actual rotation position of the control shaft 12 does not remain thesame in all situations depending, for instance, on the individualspecificity of the sensor, mechanism variations, and their changes withtime. Under these circumstances, the ECU 28 is capable, for instance, ofrotating the control shaft 12 until one of its control ends is reachedimmediately after internal combustion engine startup (this process ishereinafter referred to as a “strike process”) and calibrating itsoutput in accordance with the resulting sensor output. Therefore, theECU 28 can accurately detect the rotation position of the control shaft12 in accordance with the output from the rotation angle sensor 26without being affected by the above-mentioned changes with time and thelike.

[Detailed Configuration of the Variable Valve Mechanism]

The mechanical configuration and operation of the variable valvemechanism according to the present embodiment will now be described inrelation to individual cylinders. In the following description, themechanism is referred to as the variable valve mechanism with referencenumeral 30 assigned. It is also assumed that each cylinder of theinternal combustion engine is equipped with two intake valves and thateach variable valve mechanism 30 drives two intake valves.

FIG. 2 is an essential part perspective view of the variable valvemechanism 30, which is provided for each cylinder. The variable valvemechanism 30 is equipped with two valve bodies 32 (intake valves) thatare to be driven. A valve stem 34 is fastened to each valve body 32. Theend of the valve stem 34 is in contact with a pivot that is mounted onone end of a rocker arm 36. A valve spring (not shown in FIG. 2) workson the valve stem 34. The rocker arm 36 is pushed upward by the valvestem 34 on which the valve spring works. The other end of the rocker arm36 is supported by a hydraulic lash adjuster 38 in a movable state. Bymeans of automatically adjusting the rocker arm's vertical position byhydraulic pressure, the hydraulic lash adjuster 38 automatically adjustsa tappet clearance.

A roller 40 is positioned at the central part of the rocker arm 36. Aswinging arm 42 is positioned over the roller 40. The configurationaround the swinging arm 42 will now be described with reference to FIG.3.

FIG. 3 is an exploded perspective view illustrating a first arm member44 and a second arm member 46. The first arm member 44 and second armmember 46 are major component members of the variable valve mechanism30, which is shown in FIG. 2. The aforementioned swinging arm 42 is apart of the first arm member 44.

As shown in FIG. 3, the first arm member 44 incorporates two swingingarms 42 and a roller contact surface 48, which is sandwiched between thetwo swinging arms 42. The two swinging arms 42 are provided respectivelyfor the two valve bogies 32 and in contact with the aforementionedroller 40 (see FIG. 2).

The first arm member 44 is equipped with a bearing section 50. Thebearing sections 50 are provided so as to penetrate the swinging arms,respectively. Each swinging arm 42 has a concentric circular section 52and a pushing pressure section 54 at a surface that is in contact withthe roller 40. The concentric circular section 52 is provided such thatthe surface in contact with the roller 40 is concentric with the bearingsection 50. The pushing pressure section 54 is provided such that thedistance between the center of the bearing section 50 and a specificposition thereon becomes longer as the specific position becomes closerto its leading end.

The second arm member 46 is equipped with a non-swinging section 56 anda swinging roller section 58. The non-swinging section 56 is providedwith a through-hole. The control shaft 12, which is described withreference to FIGS. 1A and 1B, is inserted into the through-hole.Further, a retaining pin 62 is inserted into the non-swinging section 56and control shaft 12 in order to lock the positional relationshipbetween the non-swinging section 56 and control shaft 12. Therefore, thenon-swinging section 56 and control shaft 12 function as a one solidpiece.

The swinging roller section 58 is provided with two sidewalls 64. Thesidewalls 64 are joined to the non-swinging section 56 via the rotationshaft 66 so that the sidewalls 64 freely turn. A cam contact roller 68and a slide roller 70 are positioned between the two sidewalls 64. Thecam contact roller 68 and slide roller 70 can freely turn while they aresandwiched between the sidewalls 64.

The aforementioned control shaft 12 is retained by the bearing section50 of the first arm member 44 so that the control shaft 12 can rotate.In other words, the control shaft 12 should be integral with thenon-swinging section 56 while it is retained by the bearing section 50.To meet such a requirement, the non-swinging section 56 (that is, thesecond arm member 46) is positioned between the two swinging arms 42 ofthe first arm member 44 before being secured to the control shaft 12.While such positioning is achieved, the control shaft 12 is inserted soas to pass through the two bearing sections 50 and non-swinging section56. Subsequently, the retaining pin 62 is set so as to secure thecontrol shaft 12 and non-swinging section 56. As a result, there isprovided a mechanism in which the first arm member 44 can freely turn onthe control shaft 12, the non-swinging section 56 is integral with thecontrol shaft 12, and the swinging roller section 58 can swing inrelation to the non-swinging section 56.

When the first arm member 44 and second arm member 46 are assembled asdescribed above, the slide roller 70 of the swinging roller section 58can come into contact with the roller contact surface 48 of the firstarm member 44 as long as the relative angle between the first arm member44 and control shaft 12, that is, the relative angle between the firstarm member 44 and non-swinging section 56 is within a range satisfying apredefined condition. When the first arm member 44 turns on the controlshaft 12 within the range that satisfies the predefined condition whilethe slide roller 70 of the swinging roller section 58 is in contact withthe roller contact surface 48 of the first arm member 44, the slideroller 70 can roll along the roller contact surface 48. The variablevalve mechanism according to the present embodiment opens or closes thevalve body 32 while operating with the roll of the slide roller 70. Theoperation of the valve body 32 will be described in detail later withreference to FIGS. 4A, 4B, 5A, and 5B.

FIG. 2 shows the assembled state that is provided by the first armmember 44, second arm member 46, and control shaft 12 are assembledtogether by the aforementioned manner. In such an assembled state, thepositions of the first arm member 44 and second arm member 46 areregulated by the rotation position of the control shaft 12. As describedearlier, the motor 22 is coupled to the control shaft 12 via a gearmechanism (see FIGS. 1A and 1B). In the state shown in FIG. 2, therotation angle of the control shaft 12 is adjusted by the motor 22 sothat the slide roller 70 is brought into contact with the roller contactsurface 48.

The variable valve mechanism according to the present embodimentincludes a camshaft 72 that rotates in synchronism with a crankshaft. Asis the case with the control shaft 12, the camshaft 72 is retained bybearings fastened to the cylinder head 10 so that the camshaft 72 canrotate. A cam 74, which is provided for each internal combustion enginecylinder, is fastened to the camshaft 72. In a state shown in FIG. 2,the cam 74 is in contact with the cam contact roller 68 so that theupward motion of the swinging roller section 58 is regulated. In otherwords, the roller contact surface 48 of the first arm member 44 ismechanically coupled to the cam 74 via the cam contact roller 68 andslide roller 70 of the swinging roller section 58 in the state shown inFIG. 2.

When a cam nose presses the cam contact roller 68 while the cam 74rotates in the state described above, the applied pressure istransmitted to the roller contact surface 48 via the slide roller 70.While rolling on the roller contact surface 48, the slide roller 70 cancontinuously transmit the force of the cam 74 to the first arm member44. As a result, the first arm member 44 rotates on the control shaft12, thereby causing the swinging arm 42 to depress the rocker arm 36 andthe valve body 32 to move in the valve opening direction. As describedabove, the variable valve mechanism 30 can operate the valve body 32 bytransmitting the force of the cam 74 to the roller contact surface 48via the cam contact roller 68 and slide roller 70.

[Operation of the Variable Valve Mechanism]

The operation of the variable valve mechanism 30 will now be describedwith reference to FIGS. 4A, 4B, 5A, and 5B. In FIGS. 4A, 4B, 5A, and 5B,a lost motion spring 76 and a valve spring 78 are shown in addition tothe aforementioned components. As described earlier, the valve spring 78pushes the valve stem 34 and rocker arm 36 in the valve closingdirection. The lost motion spring 76, on the other hand, maintainsmechanical contact between the roller contact surface 48 and cam 74.

As described above, the variable valve mechanism 30 drives the valvebody 32 by mechanically transmitting the force of the cam 74 to theroller contact surface 48. For proper operation of the variable valvemechanism 30, it is therefore necessary that the cam 74 be mechanicallycoupled to the roller contact surface 48 at all times via the camcontact roller 68 and slide roller 70. To meet this requirement, it isnecessary that the roller contact surface 48, that is, the first armmember 44, be pushed toward the cam 74.

The lost motion spring 76 used in the present embodiment is installed sothat its upper end is fastened, for instance, to the cylinder head withthe lower end positioned to push the rear end of the roller contactsurface 48. The pushing force works so that the roller contact surface48 pushes the slide roller 70 upward. Further, the pushing force alsoworks to press the cam contact roller 68 against the cam 74. As aresult, the variable valve mechanism 30 ensures that the cam 74 ismechanically coupled to the roller contact surface 48.

FIGS. 4A and 4B show that the variable valve mechanism 30 operates togive a small lift to the valve body 32. This operation is hereinafterreferred to as a “small lift operation”. More specifically, FIG. 4Aindicates that the valve body 32 is closed during the small liftoperation, whereas FIG. 4B indicates that the valve body 32 is openduring the small lift operation.

In FIG. 4A, the symbol θ_(c) denotes a parameter that indicates therotation position of the control shaft 12. The parameter is hereinafterreferred to as the “control shaft rotation angle θ_(c)”. For the sake ofconvenience, the control shaft rotation angle θ_(c) is defined herein asthe angle between the vertical direction and the axial direction of theretaining pin 62 that secures the control shaft 12 and non-swingingsection 56. The symbol θ_(A) in FIG. 4A denotes a parameter thatindicates the rotation position of the swinging arm 42. This parameteris hereinafter referred to as the “arm rotation angle θ_(A)”. For thesake of convenience, the arm rotation angle θ_(A) is defined herein asthe angle between the horizontal direction and the straight lineconnecting the leading end of the swinging arm 42 to the center of thecontrol shaft 12.

In the variable valve mechanism 30, the rotation position of theswinging arm 42, that is, the arm rotation angle θ_(A), is determined bythe position of the slide roller 70. The position of the slide roller 70is determined by the position of the rotation shaft 66 for the swingingroller section 58 and the position of the cam contact roller 68. Withinthe range within which the contact between the cam controller roller 68and cam 74 is maintained, the greater the degree of counterclockwiserotation of the rotation shaft 66 becomes in FIGS. 4A and 4B, that is,the greater the control shaft rotation angle θ_(c) is, the higher theposition of the slide roller 70 changes. In the variable valve mechanism30, therefore, the greater the control shaft rotation angle θ_(c) is,the smaller the arm rotation angle θ_(A) becomes.

In a state shown in FIG. 4A, the control shaft rotation angle θ_(c) ismaximized within the range within which the cam contact roller 68 canmaintain its contact with the cam 74, that is, the cam 74 can regulatethe upward movement of the cam contact roller 68. Therefore, the armrotation angle θ_(A) is nearly minimized in the state shown in FIG. 4A.In this instance, the variable valve mechanism 30 is such that theapproximate center of the concentric circular section 52 of the swingingarm 42 is in contact with the roller 40 of the rocker arm 36, therebyclosing the valve body 32. The arm rotation angle θ_(A) prevailing inthis instance is hereinafter referred to as the “reference arm rotationangle θ_(A0) for a small lift”.

When the cam 74 rotates in the state shown in FIG. 4A, the cam contactroller 68 moves toward the control shaft 12 as it is pressed by the camnose. Since the distance between the rotation shaft 66 of the swingingroller section 58 and the slide roller 70 remains unchanged, the rollercontact surface 48 is depressed by the slide roller 70, which rollsabove the roller contact surface 48, when the cam contact roller 68approaches the control shaft 12. Consequently, the swinging arm 42rotates in such a direction as to increase the arm rotation angle θ_(A).As a result, the contact point between the swinging arm 42 and roller 40leaves the approximate center of the concentric circular section 52 andmoves toward the pushing pressure section 54.

When the pushing pressure section 54 comes into contact with the roller40 due to the rotation of the swinging arm 42, the valve body 32 movesin the valve opening direction in spite of the force applied by thevalve spring 78. When the vertex of the cam nose comes into contact withthe cam contact roller 68 as shown in FIG. 4B, the arm rotation angleθ_(A) becomes maximized (this angle is hereinafter referred to as the“maximum arm rotation angle θ_(AMAX)). Consequently, the lift amount forthe valve body 32 reaches its maximum. Subsequently, with the rotationof cam 74, the arm rotation angle θ_(A) decreases, thereby the liftamount for the valve body 32 decreases. When the contact point betweenthe roller 40 and swinging arm 42 returns to the concentric circularsection 52, the valve body 32 closes.

Since the reference arm rotation angle θ_(A0) for a small lift operationis small, the valve body 32 remains closed for a certain period of timeafter the cam nose begins to come into contact with the cam contactroller 68. After the maximum lift amount is generated, the valve body 32reverts to a closed state relatively early before the end of cam nosepressure application to the cam contact roller 68. As a result, when asmall lift operation is performed, the time in which the valve body 32is in a non-closed state is small, that is, the operating angle of thevalve body 32 is small. As well, the maximum lift amount for the valvebody 32 is small in this case.

FIGS. 5A and 5B indicate that the variable valve mechanism 30 operatesto give a great lift to the valve body 32. This operation is hereinafterreferred to as a “great lift operation”. More specifically, FIG. 5Aindicates that the valve body 32 is closed during a great liftoperation, whereas FIG. 5B indicates that the valve body 32 is openduring a great lift operation.

When a great lift operation is to be performed, the control shaftrotation angle θ_(c) is adjusted to a sufficiently small value as shownin FIG. 5A. As a result, the arm rotation angle θ_(A) for anon-liftstate, that is, the reference arm rotation angle θ_(A0), is set to asufficiently great value to such an extent that the slide roller 70 doesnot fall away from the roller contact section 28. The variable valvemechanism 30 is configured so that the contact point between theswinging arm 42 and roller 40 is positioned at the end of the concentriccircular section 52 at the above reference arm rotation angle θ_(A0). Insuch a situation, therefore, the valve body 32 remains closed.

When the cam 74 rotates in a state shown in FIG. 5A, the contact pointbetween the roller 40 and swinging arm 42 moves from the concentriccircular section 52 to the pushing pressure section 54 immediately afterthe cam contact roller 68 begins to be pressed by the cam nose. Thevalve body 32 is then greatly pushed in the valve opening directionuntil the cam contact roller 68 is pressed by the peak section of thecan nose. Even after the lift amount for the valve body 32 is maximizedas shown in FIG. 5B, the valve body 32 remains open for a long period oftime as far as the cam contact roller 68 is pressed by the cam nose.Therefore, while the great lift operation is being performed asdescribed above, the variable valve mechanism 30 can provide the valvebody 32 with a great operating angle and large lift amount.

[Problems with the Variable Valve Mechanism According to the PresentEmbodiment]

As described earlier, the variable valve mechanism according to thepresent embodiment can change the operating angle and lift amount of thevalve body 32 by rotating the control shaft 12. In the presentembodiment, the control shaft 12 and camshaft 72 are both retained bythe cylinder head 10. In FIG. 4A, distance L represents the dimensionbetween the control shaft 12 and camshaft 72. Distance L changes whenthe cylinder head 10 thermally deforms due to a temperature change inthe area around the cylinder head 10. When a temperature change occursin the area around the cylinder head 10, the members positioned betweenthe control shaft 12 and camshaft 72, namely, the first arm member 44and second arm member 46, are subject to thermal expansion or shrinkage.

The cylinder head 10 according to the present embodiment is made of analuminum-based material. On the other hand, the first arm member 44 andsecond arm member 46 are made of an iron-based material. These materialsexhibit different linear expansion coefficients. Therefore, if theambient temperature of the cylinder head 10 changes, the resultingstatus is the same as that is invoked by a change in distance L.

More specifically, if the temperature is increased, distance L increasesto a greater extent than the expansion of the first arm member 44 andsecond arm member 46, and the reference arm rotation angle θ_(A0)decreases, thereby decreasing the actual operating angle. If, on thecontrary, the temperature prevailing in the area around the cylinderhead 10 is decreased, distance L decreases to a greater extent that theshrinkage of the first arm member 44 and second arm member 46, and thereference arm rotation angle θ_(A0) increases, thereby increasing theactual operating angle.

FIG. 6 illustrates the actual operating angle's temperaturecharacteristic that is based on the linear expansion coefficientdifference between the member determining distance L and the memberpositioned between the control shaft 12 and cam 74. The actual operatingangle indicated by a broken line in FIG. 6 is an operating angle that iscalculated by substituting the output of the rotation angle sensor 26into a reference arithmetic expression. In other words, it is an actualoperating angle that is provided at a reference temperature for settingup the reference arithmetic expression. This operating angle ishereinafter referred to as the “detected operating angle”.

If the ECU 28 calculates the operating angle of the valve body 32 byconstantly substituting the output of the rotation angle sensor 26 intothe reference arithmetic expression, the resulting calculated detectedoperating angle is smaller than the actual operating angle in alow-temperature region and greater than the actual operating angle in ahigh-temperature region as shown in FIG. 6. Therefore, if such acalculation method is used, a desired operating angle or lift amountcannot accurately be obtained even when control is exercised with thecontrol shaft rotation angle θ_(c) set as a target value. If, in athrottle-less internal combustion engine, the intake valve's operatingangle or lift amount deviates from a desired value, the intake airamount control accuracy is adversely affected.

The deviation between the actual operating angle and detected operatingangle is a value that is determined primarily by the ambient temperatureof the cylinder head 10. Therefore, when the ambient temperature isdetermined, it is possible to estimate the deviation between the actualoperating angle and detected operating angle. As such being the case,the variable valve mechanism according to the present embodimentestimates the ambient temperature of the cylinder head 10 in accordancewith the output of the water temperature sensor 29 (cooling watertemperature THW), and calculates the deviation, which will possiblyarise between the detected operating angle and actual operating angle,in accordance with the estimated ambient temperature. Further, thevariable valve mechanism according to the present embodiment calculatesthe actual operating angle by adding the calculated deviation to thedetected operating angle as a correction value.

FIG. 7 is a flowchart illustrating a routine that the ECU 28 executes inaccordance with the present embodiment, which implements the abovefunctionality. The routine shown in FIG. 7 first detects the coolingwater temperature THW of the internal combustion engine in accordancewith the output of the water temperature sensor 29 (step 80). Thepresent embodiment handles the detected cooling water temperature THW asthe ambient temperature of the cylinder head 10.

Next, step 82 is performed to calculate the correction value for theoperating angle. The ECU 28 stores a map, which defines the relationshipbetween the ambient temperature of the cylinder head 10 and thedeviation Δθ between the actual operating angle and detected operatingangle (Δθ= actual operating angle−detected operating angle), that is,the value indicated as the correction value” in FIG. 6. In step 82, themap is referenced to calculate the deviation Δθ for the currenttemperature. The calculated deviation Δθ is then handled as theoperating angle correction value.

Next, step 84 is performed to detect the output of the rotation anglesensor 26. Step 86 is then performed to calculate the detected operatingangle in accordance with the detected sensor output. The ECU 28 storesthe reference arithmetic expression for converting the output of therotation angle sensor 26 to the detected operating angle. In step 86,the detected operating angle is calculated in accordance with the storedreference arithmetic expression. According to the process performed instep 86, it is possible to calculate an operating angle that isindicated by a broken line in FIG. 6, that is, the actual operatingangle that occurs at the reference temperature.

Next, step 88 is performed to calculate the actual operating angle byadding the operating angle correction value to the detected operatingangle that has been calculated as described above. The process performedin step 88 calculates the actual operating angle that is indicated by asolid line in FIG. 6.

Subsequently to the above process, the ECU 28 exercises feedback controlso that the operating angle of the valve body 32 is handled as a targetoperating angle (step 90). More specifically, the control value for themotor 22 is controlled so that the actual operating angle calculated instep 88 above accords with the target operating angle calculated byanother routine in accordance, for instance, with the required intakeair amount.

The above process makes it possible to avoid the influence of atemperature change in the area around the cylinder head 10 and calculatethe actual operating angle provided by the valve body 32 accurately atall times. Further, the operating angle and lift amount of the valvebody 32 can be accurately controlled by controlling the control valuefor the motor 22 on the basis of the accurate actual operating angle.Therefore, the variable valve mechanism according to the presentembodiment can control the valve opening characteristic of the intakevalve accurately at all times and constantly provide a throttle-lessinternal combustion engine with an excellent operating characteristicwithout regard to the internal combustion engine warm-up status orenvironmental conditions.

Strictly speaking, in the variable valve mechanism according to thepresent embodiment, the relationship between the temperature and thedeviation Δθ between the actual operating angle and detected operatingangle may vary with the actual operating angle. It is thereforedifficult to provide a precise operating angle correction for alloperating angles depending on the deviation Δθ-temperature map stored inthe ECU 28.

Under these circumstances, the present embodiment prepares a deviationΔθ-temperature map for a situation where the smallest operating angle isrequired for the valve body 32, that is, where a small lift operation isperformed as described with reference to FIGS. 4A and 4B. According tothe prepared map, it is possible to provide corrections with adequateaccuracy in a region where the operating angle and lift amount are smallalthough the required operating angle correction accuracy decreases in aregion where the required operating angle and lift amount are large.

In a region where the operating angle and lift amount are small, aslight error in the operating angle incurs a great error in the intakeair amount. In a region where the operating angle and lift amount arelarge, on the other hand, a certain error in the operating angle doesnot incur a significant error in the intake air amount. Therefore, theuse of a deviation Δθ-temperature map for a small lift operation makesit possible to control the intake air amount with adequate accuracy inall operating angle regions although it lowers the operating anglecorrection accuracy in a great lift region.

To attain high correction accuracy for all operating angles, analternative is to prepare a map in which the deviation Δθ between theactual operating angle and detected operating angle are defined based ontemperature and operating angle, and reference the map in step 82 tocalculate the deviation Δθ, that is, the operating angle correctionvalue Δθ. When this method is used, excellent operating angle/liftamount control can be exercised in all operating angle regions althoughan increased computation load is imposed on the ECU 28.

The first embodiment, which has been described above, corrects thedetected operating angle in accordance with the ambient temperature ofthe cylinder head 10 to obtain the actual operating angle and thenaccordingly corrects the control value to be supplied to the motor 22.However, the correction target is not limited to the operating angle orthe control value for the motor 22. More specifically, the targetoperating angle, which is the target for the actual operating angle infeedback control, may be targeted for correction. The routine shown inFIG. 7 may calculate a correction value for the target operating anglein step 82, calculate a corrected target operating angle in step 88, andcontrol the motor 22 so that the detected operating angle coincides withthe corrected target operating. angle.

The first embodiment, which has been described above, avoids theinfluence of an intake valve characteristic change arising out of atemperature change by correcting the operating angle. However, analternative method may be used to avoid such influence. For example, inanticipation that the operating angle will change in accordance with atemperature change, the fuel injection amount for each cylinder may becorrected so as to obtain a desired air-fuel ratio in relation to anintake air amount that is provided by the resulting operating angle.

The first embodiment, which has been described above, has aconfiguration that changes the operating angle and lift amount of thevalve body 32 by rotating the control shaft 12. However, the presentinvention is not limited to the use of such a method. Alternatively, theoperating angle and lift amount of the valve body 32 may be changed bysliding the control shaft.

In the first embodiment, which has been described above, the variablevalve mechanism 30 changes both the operating angle and lift amount inaccordance with the status of the control shaft 12. However, the presentinvention is not limited to the use of such a method. Alternatively, thevariable valve mechanism may change either the operating angle or liftamount. If such an alternative method is used, the correction foravoiding the influence of temperature may be made while focusingattention on either the operating angle or lift amount, whichever isabout to change.

In the first embodiment, which has been described above, the first armmember 44 and second arm member 46 correspond to the “adjustmentmechanism” according to the aforementioned first aspect of the presentinvention. The water temperature sensor 29 corresponds to the“temperature detection unit” according to the first aspect of thepresent invention. The “temperature correction unit” according to thefirst aspect of the present invention is implemented when the ECU 28performs processing steps 80 through 90.

In the first embodiment, which has been described above, the rotationangle sensor 26 corresponds to the “sensor” according to theaforementioned second aspect of the present invention. The motor 22corresponds to the “actuator” according to the second aspect of thepresent invention. The “actuator control unit” and “temperaturecorrection unit” according to the second or third aspect of the presentinvention are implemented when the ECU 28 performs processing step 90.

In the first embodiment, which has been described above, the rotationangle sensor 26 corresponds to the “sensor” according to theaforementioned fourth aspect of the present invention. The motor 22corresponds to the “actuator” according to the fourth aspect of thepresent invention. The “target status setup unit” according to thefourth aspect of the present invention is implemented when the ECU 28sets a target operating angle for feedback control. The “temperaturecorrection unit” according to the fourth aspect of the present inventionis implemented when the ECU 28 corrects the target operating angle inaccordance with temperature. The “actuator control unit” according tothe fourth aspect of the present invention is implemented when the ECU28 exercises feedback control over the motor 22 with the correctedtarget operating angle set as a control target.

Second Embodiment

A second embodiment of the present invention will now be described withreference to FIGS. 1A through 5B. The variable valve mechanism accordingto the second embodiment has the same structure as the variable valvemechanism according to the first embodiment. As regards the mechanismaccording to the first embodiment, the member for determining thedistance between the control shaft 12 and camshaft 72, that is, distanceL shown in FIG. 4A, and the member positioned between the control shaft12 and camshaft 72 are made of materials having different linearexpansion coefficients, and the operating angle is corrected inaccordance with the ambient temperature of the cylinder head 10 to avoidthe influence of thermal expansion and thermal shrinkage.

As regards the variable valve mechanism according to the secondembodiment, however, the members for determining distance L (that is,the cylinder head 10) and the member positioned between the controlshaft 12 and camshaft 72 (namely, the first arm member 44 and second armmember 46) are made of materials having the same linear expansioncoefficient in order to avoid the influence of thermal expansion andthermal shrinkage. This configuration can be achieved when, forinstance, the cylinder head 10 is made of an iron-based material as isthe case with the first arm member 44 and second arm member 46.

If the cylinder head 10, first arm member 44, and second arm member 46are made of materials having the same linear expansion coefficient, thesame expansion/shrinkage occurs in a mechanism between the control shaft12 and camshaft 72 as for distance L when distance L expands or shrinksdue to a temperature change. Even if the ambient temperature of thecylinder head 10 changes in the above instance, the basic arm rotationangle θ_(A0) remains unchanged. Therefore, the relationship between theoperating angle of the valve body 32 and the control shaft rotationangle θ_(c) does not change. As a result, the variable valve mechanismaccording to the present embodiment can constantly provide the valvebody 32 with a desired valve opening characteristic without beingaffected by a temperature change and without having, for instance, tocorrect the operating angle.

In the second embodiment, which has been described above, the first armmember 44 and second arm member 46 correspond to the “adjustmentmechanism” and the “member positioned between the control shaft and cam”according to the aforementioned fifth aspect of the present invention.The cylinder head 10 corresponds to the “member for determining thedistance between the control shaft and cam” according to the fifthaspect of the present invention.

Third Embodiment

A third embodiment of the present invention will now be described withreference to FIGS. 8 through 10. The variable valve mechanism accordingto the third embodiment has the same structure as the variable valvemechanism according to the first embodiment.

[Problems with the Variable Valve Mechanism according to the PresentEmbodiment]

It is necessary that the operating angle and lift amount for properlyoperating the internal combustion engine be properly set in accordancewith the internal combustion engine's operating status. Morespecifically, it is necessary that the operating angle and lift amountsuitable for startup be set at the time of internal combustion enginestartup. When the internal combustion engine is stopped, however, theoperating angle and lift amount may not always be set as appropriate forinternal combustion engine startup. For an internal combustion engineequipped with a variable valve mechanism, therefore, it is necessarythat the operating angle and lift amount be corrected during the timeinterval between the instant at which an internal combustion engine stopis requested and the instant at which the internal combustion enginerestarts.

The conventional variable valve mechanism shown in Japanese PatentLaid-Open No. 63023/1995 discussed above can correct the valve body'soperating angle and lift amount by rotating the control shaft.Therefore, an excellent startup characteristic can be obtained as far asan internal combustion engine startup sequence is initiated afteradjusting the control shaft rotation position in compliance with arequest for internal combustion engine startup to provide the operatingangle and lift amount suitable for startup.

To adjust the control shaft rotation position, however, it is necessaryto detect it. Further, the relationship between the output of anemployed sensor, which is necessary for control shaft rotation positiondetection, and the actual rotation position may vary with the individualspecificities of the sensor and variable valve mechanism or with theirchanges with time. To properly adjust the control shaft rotationposition at internal combustion engine startup, therefore, it isnecessary to use a sensor output whose correlation with the controlshaft status is properly corrected.

The relationship between the control shaft rotation position and thesensor output for control shaft rotation position detection can becalibrated, for instance, by rotating the control shaft until it reachesits movement end and reading the resulting sensor output. When theinternal combustion engine starts up, however, the sensor output cannotbe calibrated in the above manner due to time limitations. Therefore, anappropriate method for satisfying the above requirements would be tocalibrate the sensor output after internal combustion engine startup,detect the sensor output at the time when an internal combustion enginestop is requested as a value prevailing control shaft rotation position(or valve body operating angle or lift amount) of the time, and adjustthe control shaft for startup on the basis of the detected sensoroutput.

However, the variable valve mechanism is usually subjected to asignificant change in ambient temperature after an internal combustionengine stop. Therefore, the parts around the control shaft and camshaftare likely to suffer significant thermal deformation after an internalcombustion engine stop. If such thermal deformation occurs in thevariable valve mechanism, a status change occurs in the swinging arm,which is positioned between the control shaft and cam, and in theadjustment mechanism for changing the swinging arm angle.

More specifically, in the conventional variable valve mechanismdescribed above, when the ambient temperature of the control shaftlowers, the spacing interval between the control shaft and camshaftdecreases, thereby the status of the swinging arm is changed in thedirection of increasing the operating angle and lift amount. If, on theother hand, the ambient temperature of the control shaft rises, thespacing interval between the control shaft and camshaft increases,thereby changing the status of the swinging arm in the direction ofdecreasing the operating angle and lift amount. Therefore, regarding aninternal combustion engine equipped with a variable valve mechanism,even if the sensor output is acquired at a time of an engine stop andthe control shaft is adjusted for startup on the basis of the acquiredsensor output, it becomes that the control shaft status prevailing atstartup is shifted from an optimum operating angle/lift amountgeneration state by the amount due to a temperature change encounteredafter the internal combustion engine stop.

The variable valve mechanism according to the present embodiment hasbeen made to solve the above problems. It is an object of the presentembodiment to provide a variable valve mechanism that is capable ofconstantly providing the valve body with an optimum valve openingcharacteristic at internal combustion engine startup without beingaffected by a temperature change that occurs after an internalcombustion engine stop.

Same as in the first embodiment, the variable valve mechanism accordingto the present embodiment can change the operating angle and lift amountof the valve body 32 by rotating the control shaft 12. When theoperating angle and lift amount are optimized, the internal combustionengine according to the present embodiment can obtain a desired intakeair amount and a desired operating state.

To properly start up the internal combustion engine, it is necessary toprovide the valve body 32 with an operating angle and lift amountsuitable for startup at the time of startup. Since it is demanded thatthe internal combustion engine exhibit excellent startability within theentire assumable operating temperature range, it is necessary that theoperating angle and lift amount be set at internal combustion enginestartup so as to obtain excellent startability under the most severeconditions. The present embodiment assumes that the lower limit of theoperating temperature range for the internal combustion engine is −35°C. Therefore, the operating angle and lift amount for startup should becontrolled so that the internal combustion engine properly starts up inan environment where the temperature is −35° C. The operating anglerange that meets the above requirement is hereinafter referred to as the“operating angle range required for extremely cold startup”.

While the internal combustion engine is running, the operating angleappropriate for the operating state is constantly achieved. When arequest for stopping the internal combustion engine is generated,therefore, the operating angle is usually outside the operating anglerange required for extremely cold startup. To start up the internalcombustion engine with the operating angle maintained within theoperating angle range required for extremely cold startup, it isnecessary to correct the rotation position of the control shaft 12 sothat the operating angle falls within the operating angle range requiredfor extremely cold startup during the time interval between the instantat which an internal combustion engine stop is requested and the instantat which the actual startup sequence is initiated.

As described earlier, the variable valve mechanism according to thepresent embodiment includes the rotation angle sensor 26, which detectsthe rotation position of the control shaft 12. Therefore, the ECU 28 canproperly correct the rotation position of the control shaft 12 bycontrolling the motor 22 while observing the output of the rotationangle sensor 26. However, the relationship between the output of therotation angle sensor 26 and the actual operating angle is not alwaysabsolute but is affected, for instance, by changes over time. Therefore,when the rotation position of the control shaft 12 is to be adjusted atinternal combustion engine startup, it is preferred that the motor 22 becontrolled on the basis of the sensor output whose correlation with theactual operating angle is assured. As viewed from the time of internalcombustion engine startup, the last time the relationship between theoutput of the rotation angle sensor 26 and the actual operating angle isassured is the last internal combustion engine stop. Therefore, foradjusting the rotation position of the control shaft 12 in preparationfor internal combustion engine startup, it is proper to detect theoutput of the rotation angle sensor 26 (that is, the operating angle) atthe time of the internal combustion engine stop and use the detectedoutput as a base data of the adjustment.

However, it is common that the ambient temperature of the variable valvemechanism 30 greatly changes after an internal combustion engine stop.Therefore, the section around the control shaft 12 and camshaft 72 islikely to suffer significant thermal deformation after an internalcombustion engine stop. If such thermal deformation occurs, therelationship between the output of the rotation angle sensor 26 and theactual operating angle of the valve body 32 changes.

As described above, distance L shown in FIG. 4A represents the dimensionbetween the control shaft 12 and camshaft 72. Distance L decreases whenthe ambient temperature of the cylinder head 10 lowers after an internalcombustion engine stop. During a process during which the ambienttemperature of the cylinder head 10 lowers, the members positionedbetween the control shaft 12 and camshaft 72, namely, the first armmember 44 and second arm member 46, are subject to thermal shrinkage.

The cylinder head 10 according to the present embodiment is made of analuminum-based material. On the other hand, the first arm member 44 andsecond arm member 46 are made of an iron-based material. These materialsexhibit different linear expansion coefficients. Therefore, when theambient temperature of the cylinder head 10 lowers, distance L decreasesto a greater extent than the first arm member 44 and second arm member46 do.

In other words, when the ambient temperature of the cylinder head 10lowers after an internal combustion engine stop within the variablevalve mechanism 30 according to the present embodiment, the resultingphenomenon is such that distance L is substantially decreased. As aresult, the swinging arm 42 rotates in the direction of increasing thearm rotation angle θ_(A) so that the actual operating angle of the valvebody 12 increases.

FIG. 8 shows the relationship between a decrease in the internalcombustion engine temperature and the actual operating angle change inthe valve body 32. In FIG. 8, point A corresponds to temperature t0 andactual operating angle A. Temperature t0 is the ambient temperature ofthe variable valve mechanism 30 during an internal combustion engineoperation. A solid straight line passing through point A in FIG. 8indicates the temperature/actual operating angle relationship thatprevails after the rotation position of the control shaft 12 is fixed atpoint A. It indicates that the temperature/actual operating anglerelationship shifts from point A to point B if the internal combustionengine temperature drops to the lowest temperature within the operatingtemperature range (it is assumed herein that the lowest temperature is−35° C.) while the control shaft 12 remains at a fixed position afterthe internal combustion engine is stopped at temperature t0 and atactual operating angle A.

The “operating angle range required for extremely cold startup”, whichis indicated by two horizontal broken lines in FIG. 8, represents anoptimum operating angle range for properly starting the internalcombustion engine at an ambient temperature as low as 35° C. To properlystart up the internal combustion engine within the operating temperaturerange at all times, it is preferred that an internal combustion enginestartup process (cranking) start while the actual operating angle of thevalve body 32 is within its “operating angle range required forextremely cold startup”. If, for instance, the temperature/actualoperating angle relationship corresponds to point B in FIG. 8, it ispreferred that cranking starts after the rotation position of thecontrol shaft 12 is adjusted so that actual operating angle B is withinthe operating angle range required for extremely cold startup.

However, while the temperature/actual operating angle relationshipshifts from point A to point B, the rotation position of the controlshaft 12 remains unchanged. Therefore, even when the actual operatingangle changes from A to B after an internal combustion engine stop, theoutput of the rotation angle sensor 26 does not change as far as theactual operating angle change is solely due to a temperature change. Inthis instance, if the actual operating angle is recognized on the basisof the output of the rotation angle sensor 28 only, the operating angleis erroneously recognized as A although it should be recognized as Bwhen the internal combustion engine restarts at an extremely lowtemperature (−35° C.).

If, in reality, the operating angle is A, the actual operating angle canbe set at value C, which is within the operating angle range requiredfor extremely cold startup, when the rotation position of the controlshaft 12 is adjusted to increase the operating angle by the amount ofdifference between the value A and the operating angle range requiredfor extremely cold startup. However, if the same adjustment is madewhile assuming that the actual operating angle value is A in a situationwhere the actual operating angle is B, the resulting actual operatingangle is represented by the value D, which is greater than the value Bby the amount equal to C minus A (see the non-horizontal broken line inFIG. 6).

Meanwhile, the dependence of the actual operating angle on thetemperature can be experimentally determined. Therefore, if temperaturet0, which prevails at the time of an internal combustion engine stop, isknown, the amount of change in the actual operating. angle (B-A), whichoccurs during a process during which the internal combustion enginetemperature lowers to an extremely low temperature (−35° C.), can bedetermined as a function of the amount of a temperature change(t0−(−35)). When actual operating angle A, which prevails during aninternal combustion engine stop, and its change amount (B-A) are bothknown, they can be added together to determine actual operating angle B,which prevails at the extremely low temperature and is implemented whilethe control shaft 12 is fixed. When actual operating angle B isdetermined, it is possible to calculate a correction value ΔVL forconverting the value B to the value E, which falls within the operatingangle range required for extremely cold startup.

When the control shaft 12 is adjusted at the time of an internalcombustion engine stop so that actual operating angle A changes to thevalue F, which is smaller by ΔVL, a situation can be generated in whichactual operating angle E is within the operating angle range requiredfor extremely cold startup if the internal combustion engine temperaturebecomes extremely low (−35° C.) in a subsequent process. In such aninstance, the internal combustion engine can be properly restarted at anextremely low temperature simply by initiating a cranking sequencewithout having to adjust the rotation position of the control shaft 12.In the present embodiment, therefore, the ECU 28 detects actualoperating angle A (the output of. the rotation angle sensor 26) andtemperature t0 (the output of the water temperature sensor 29) at thetime of an internal combustion engine stop, calculates the correctionvalue ΔVL in accordance with the detected values, and adjusts therotation position of the control shaft 12 so that the correction valueΔVL is reflected in the operating angle.

FIG. 9 is a flowchart illustrating a routine that the ECU 28 performs toimplement the above functionality. It is assumed that the routine isstarted at internal combustion engine startup. The routine first detectsactual operating angle A in accordance with the output of the rotationangle sensor 26 and detects the cooling water temperature THW inaccordance with the output of the water temperature sensor 29. Thedetected cooling water temperature THW is handled as the enginetemperature t0, that is, the ambient temperature of the variable valvemechanism 30 (step 100).

Next, step 102 is performed to judge whether a request for an internalcombustion engine stop is generated. More specifically, step 102 isperformed to judge whether the vehicle's ignition switch status ischanged from ON to OFF. If the judgment result indicates that no stoprequest is generated, the routine performs processing step 100 again.If, on the other hand, the judgment result indicates that a stop requestis generated, step 104 is performed to calculate the assumed restarttemperature of the internal combustion engine. More specifically, step104 is performed to calculate the difference (Δt=t0−(−35° C.)) betweenthe lowest temperature within the operating temperature range (−35° C.)and the current engine temperature, that is, the stop state temperaturet0.

Next, the non-corrective restart state operating angle B (see FIG. 6) iscalculated. More specifically, step 106 is performed to calculate anoperating angle that is expected to arise in reality when the ambienttemperature of the variable valve mechanism 30 lowers to the assumedrestart temperature with the rotation position of the control shaft 12left uncorrected, that is, an operating angle that is expected to ariseat an extremely low temperature (−35° C.) when the current status of thecontrol shaft 12 is maintained. The ECU 28 stores a map or arithmeticexpression (e.g., y=ax+b or other similar linear expression)representing a temperature/actual operating angle relationship thatlooks like FIG. 8. In step 106, the non-corrective restart stateoperating angle B is calculated by applying stop state actual operatingangle A and temperature difference Δt=t0−(−35° C.) to the relationship.

Next, step 108 is performed to calculate the correction value ΔVL (seeFIG. 8). More specifically, step 108 is performed to calculate thecorrection value ΔVL, which makes the non-corrective restart stateoperating angle B be within the operating angle range required forextremely cold startup. The ECU 28 stores a central value E for theoperating angle range required for extremely cold startup, and solvesthe expression B-E to calculate the correction value ΔVL.

Next, step 110 is performed to decrease the stop state operating angle Aby the correction value ΔVL and perform a process for achieving the stopstate target operating angle F (see FIG. 8). More specifically, themotor 22 is driven to adjust the rotation position of the control shaft12 so that the actual operating angle is decreased by the correctionvalue ΔVL.

When the above process terminates, the operating angle control processcomes to a stop, thereby terminating the routine shown in FIG. 9. In theabove process, actual operating angle A can be changed to the stop statetarget operating angle F at the time of an internal combustion enginestop in anticipation that the ambient temperature of the variable valvemechanism 30 will. subsequently decrease to an extremely low level (−35°C.). If, in this instance, the ambient temperature of the variable valvemechanism 30 actually lowers to an extremely low level before an attemptis made to restart the internal combustion engine, the cranking sequencecan be initiated with actual operating angle E, which falls within theoperating angle range required for extremely cold startup.

Thus, the variable valve mechanism 30 according to the presentembodiment can constantly provide the internal combustion engine withexcellent startability at an extremely low temperature. The higher thetemperature for startup is, the more excellent the internal combustionengine startability becomes. Consequently, if the employed conditionsmake it possible to obtain excellent startability at an extremely lowtemperature, excellent startability can be obtained within the entiretemperature range. As a result, the variable valve mechanism 30according to the present embodiment can properly restart the internalcombustion engine in any environment.

When the operating angle control method described above is used, therotation position adjustment for the control shaft 12, which is made inpreparation for a restart, can be terminated while the internalcombustion engine is stopped. In this instance, the cranking sequencecan be started immediately at a restart without changing the status ofthe control shaft 12. After an internal combustion engine restart isrequested, the variable valve mechanism according to the presentembodiment can therefore start a cranking sequence as needed for therestart.

However, the rotation position adjustment of the control shaft 12, whichis made in preparation for a restart, is not always made at the time ofan internal combustion engine stop. For example, the rotation positionadjustment may alternatively be made at the time when an internalcombustion engine restart is requested. FIG. 10 illustrates a processingprocedure that is to be performed in the above alternative case. If therotation position adjustment of the control shaft 12 is to be made uponreceipt of a startup request, the actual operating angle of the valvebody 32 changes along a straight line passing through point A in FIG. 10during in a process during which the engine temperature lowers after aninternal combustion engine stop. When the ambient temperature of thevariable valve mechanism 30 decreases to an extremely low level, theactual operating angle changes to B.

When stop state temperature t0 and stop state operating angle A aredetected, the use of the above method makes it possible to calculate thecorrection value ΔVL no matter whether the rotation position adjustmentof the control shaft 12 is made at the time of an internal combustionengine stop or startup. Therefore, when the correction value ΔVL iscalculated by the above method at the time of an internal combustionengine stop or startup and the rotation position of the control shaft 12is adjusted by the correction value ΔVL at internal combustion enginestartup, it is possible to change the actual operating angle from B toE, that is, it is possible to form a situation in which the actualoperating angle falls within the operating angle range required forextremely cold startup immediately after a startup request is generated.If a cranking sequence is initiated while the actual operating angle iswithin the operating angle range required for extremely cold startup, itis possible to implement a variable valve mechanism that is capable ofproviding the internal combustion engine with excellent startability atany temperature as is the case with the third embodiment.

In the third embodiment, which has been described above, the first armmember 44 and second arm member 46 correspond to the “adjustmentmechanism” according to the aforementioned sixth aspect of the presentinvention. Further, the water temperature sensor 29 corresponds to the“temperature detection unit” according to the sixth aspect of thepresent invention. Furthermore, the rotation angle sensor 26 correspondsto the “status detection sensor” according to the sixth aspect of thepresent invention. The “stop state temperature acquisition unit”according to the sixth aspect of the present invention is implementedwhen the ECU 28 detects the engine temperature t0 in step 100. The “stopstate characteristic value detection unit” is implemented when the ECU28 detects actual operating angle A. The “non-corrective restart statecharacteristic value calculation unit” according to the sixth aspect ofthe present invention is implemented when the ECU 28 performs processingstep 106. The “correction value calculation unit” according to the sixthaspect of the present invention is implemented when the ECU 28 performsprocessing step 108. The “pre-startup correction unit” according to thesixth aspect of the present invention is implemented when the ECU 28performs processing step 110.

Fourth Embodiment

A fourth embodiment of the present invention will now be described withreference to FIGS. 11 and 12. The variable valve mechanism according tothe fourth embodiment is structured the same as the variable valvemechanism according to the first embodiment. The variable valvemechanism according to the fourth embodiment has appropriatecharacteristics for use with an economy-run vehicle having a so-calledidling stop function, a hybrid automobile, and other vehiclesincorporating an internal combustion engine having an automaticstop/automatic start function. A case where the variable valve mechanismaccording to the present embodiment is used in conjunction with avehicle having an automatic stop/automatic start function will bedescribed below.

FIG. 11 illustrates a method for controlling the control shaft 12 thatis used in the variable valve mechanism according to the presentembodiment. The one-dot chain line in FIG. 11 represents therelationship that is established between the ambient temperature andactual operating angle of the variable valve mechanism 30 when therotation position of the control shaft 12 is fixed at a position thatpasses through point A. Since the variable valve mechanism 30 accordingto the present embodiment is configured the same as the variable valvemechanism according to the first embodiment, the actual operating angleof the valve body 32 exhibits the same temperature characteristic as inthe first embodiment. After the internal combustion engine is stopped,therefore, the actual operating angle of the valve body 32 changes witha decrease in the engine temperature even when the rotation position ofthe control shaft 12 is fixed.

In an economy-run vehicle or hybrid vehicle, the internal combustionengine frequently repeats an automatic stop/automatic start sequence. Itis demanded that the internal combustion engine in such a vehicleautomatically start in a comfortable manner. To meet such a demand, itis necessary that the actual operating angle of the valve body 32 becontrolled to a value that sufficiently withstands vibration and thelike at the time of internal combustion engine startup.

The “operating angle range required for restart”, which is indicated bytwo horizontal broken lines in FIG. 11, represents an operating anglerange within which the above demand is met. The operating angle rangerequired for restart is an operating angle range appropriate forinternal combustion engine startup. Therefore, while the internalcombustion engine is requested to perform a normal operation, the actualoperating angle is generally outside the operating angle range requiredfor restart. Consequently, the internal combustion engine generallystops in a state where the actual operating angle is outside theoperating angle range required for restart (e.g., in a state whereactual operating angle A prevails). To obtain excellent startability, itis necessary to adjust the rotation position of the control shaft 12during the time interval between an engine stop and an attempt torestart the engine so that actual operating angle A falls within theoperating angle range required for restart.

It is preferred that the internal combustion engine properly responds toa startup request. Excellent responsiveness is demanded particularly foran economy-run vehicle or hybrid vehicle in which a start/stop sequenceis frequently repeated. To improve the response to a startup request, itis desirable that the adjustment for confining the actual operatingangle within the operating angle range required for restart be completedprior to the generation of a startup request. Under these circumstances,the present embodiment adjusts the rotation position of the controlshaft 12 so that the actual operating angle A changed to a value withinthe operating angle range required for restart immediately after stop ofthe internal combustion engine, then the actual operating angle stayswithin the operating angle range required for restart without regard totemperature changes, as indicated by a solid polygonal line (arrow marksincluded) in FIG. 11. In this instance, since the actual operating anglealways remains within the operating angle range required for restart, anautomatic start can be quickly achieved simply by initiating a crankingsequence immediately whenever an internal combustion engine automaticstart is requested.

FIG. 12 is a flowchart illustrating a routine that the ECU 28 accordingto the present embodiment performs to implement the above functionality.It is assumed that the routine is initiated when the system for aneconomy-run or hybrid vehicle starts up. The routine first detectsactual operating angle A in accordance with the output of the rotationangle sensor 26 and the cooling water temperature THW in accordance withthe output of the water temperature sensor 29. The detected coolingwater temperature THW is handled as the engine temperature t0, that is,the ambient temperature of the variable valve mechanism 30 (step 120).

Next, step 122 is performed to judge whether a request for an internalcombustion engine stop is generated. If the judgment result indicatesthat no engine stop request is generated, the routine performsprocessing step 120 again. If, on the other hand, the judgment resultindicates that an engine stop request is generated, step 124 isperformed to judge whether a request for a vehicle system stop isgenerated. If the judge result indicates that a request for a vehiclesystem stop is generated, the routine immediately terminates the currentprocessing cycle. If, on the other hand, the judgment result indicatesthat no request is generated for a vehicle system stop, step 126 isperformed to judge whether a request for an internal combustion enginerestart is generated.

When a request for an internal combustion engine stop is generated, thesystem according to the present embodiment brings the internalcombustion engine to an automatic stop. If a request for an internalcombustion engine restart is generated later, the system automaticallystarts up the internal combustion engine. Therefore, the internalcombustion engine is kept stopped during the time interval between theinstant at which the request for an engine stop is recognized in step122 and the instant at which the request for a restart is recognized.During such a time interval, the ambient temperature of the variablevalve mechanism 30 continuously lowers while processing steps 128 andbeyond are performed inside the ECU 28 as described below.

In the above instance, the ECU 28 first detects the current coolingwater temperature THW as the stop period temperature t1 of the internalcombustion engine (step 128). Next, step 130 is performed to calculatethe difference between the stop state temperature t0 and the stop periodtemperature t1, that is, the temperature difference (Δt=t0−t1) that hasarisen in the temperature around the variable valve mechanism 30 afteran internal combustion engine stop.

Next, step 132 is performed to calculate the amount of an operatingangle change ΔA that has possibly occurred in the actual operating angleafter an internal combustion engine stop. The ECU 28 stores a map orarithmetic expression (e.g., y=ax+b or other similar linear expression)representing a temperature/actual operating angle relationship thatlooks like FIG. 11. In step 132, the operating angle change amount ΔA iscalculated by applying the temperature difference (Δt=t0−t1) to therelationship.

Next, step 134 is performed to judge whether A+ΔA is equal to or largerthan the lower-limit value α of the operating angle range required forrestart and equal to or lower than the upper-limit value β of theoperating angle range required for restart. If the actual operatingangle is changed by ΔA after an internal combustion engine stop, it canbe estimated that the current actual operating angle is equal to A+ΔA,which is calculated by adding the operating angle change amount ΔA tothe stop state operating angle A. More specifically, step 134 isperformed to judge whether its actual operating angle A+ΔA is within theoperating angle range required for restart.

While the internal combustion engine is stopped, the actual operatingangle A is often outside the operating angle range required for restart.Further, immediately after an internal combustion engine stop, thegenerated operating angle change amount ΔA is not enough to cancel thedeviation of the actual operating angle A from the operating angle rangerequired for restart. At the above timing, therefore, the condition ofstep 134 is not generally satisfied. In such an instance, the differencebetween the latest actual operating angle A+ΔA and the middle value ofthe operating angle range required for restart is calculated as thecorrection value ΔVL=(A+ΔA)−{(α+β)/2} (Step 136).

Next, the rotation position of the control shaft 12 is adjusted tochange the actual operating angle by the correction value ΔVL so thatthe new actual operating angle is equal to A+ΔA−ΔVL. The resultingactual operating angle (A+ΔA−ΔVL) is then stored as the latest actualoperating angle A (step 138). Further, if the above adjustment is made,the currently detected stop period temperature t1 is stored anew as thenew temperature t0 (step 140). Subsequently, processing steps 124 andbeyond are performed again.

When the above process is performed, the actual operating angle A can bechanged to the middle value of the operating angle range required forrestart immediately after the internal combustion engine is brought toan automatic stop. It is also possible to store the resulting latestactual operating angle as the new actual operating angle A and thetemperature prevailing at the time of such a change as the newtemperature t0.

Subsequently, processing steps 128 through 140, which have beendescribed above, are repeatedly performed as far as the system for aneconomy-run or hybrid vehicle itself is not stopped and no request isgenerated for an internal combustion engine restart. In this instance,step 130 is performed to calculate the difference between thetemperature t0 prevailing when the control shaft 12 is adjusted and thecurrent stop period temperature t1 as the temperature difference Δt.Further, step 134 is performed to calculate the sum of the actualoperating angle A achieved by adjusting the control shaft 12 and theoperating angle change ΔA invoked after such an adjustment as the latestactual operating angle A+ΔA, and judge whether the calculated latestactual operating angle A+ΔA is within the operating angle range requiredfor restart.

Immediately after the control shaft 12 is adjusted, the resultingoperating angle change amount ΔA is not great. Therefore, the latestactual operating angle A+ΔA is within the operating angle range requiredfor restart. In this instance, the condition of step 134 is denied, andthen steps 124 and beyond are performed again. If an adequate amount oftime elapses after the control shaft 12 is adjusted, the stop periodtemperature t1 drops so that the latest actual operating angle A+ΔA isoutside the operating angle range required for restart again. In thisinstance, the specified condition is not met in step 134 so that therotation position of the control shaft 12 is adjusted again (steps 136through 140).

When the above process is repeated, the actual operating angle stayswithin the operating angle range required for restart while the internalcombustion engine is brought to an automatic stop. Therefore, when arestart request is generated after the internal combustion engine isbrought to an automatic stop, the variable valve mechanism according tothe present embodiment can properly restart the internal combustionengine with excellent responsiveness. After an internal combustionengine restart is requested, the routine shown in FIG. 12 performs step126 to judge the specified condition is met, and then repeats processingsteps 120 and beyond.

The fourth embodiment, which has been described above, gives priority toresponsiveness for a restart. Therefore, the fourth embodiment assumesthat the actual operating angle stays within the operating angle rangerequired for restart while the internal combustion engine is stopped.However, the present invention is not limited to such an assumption. Forexample, the actual operating angle may alternatively fall within theoperating angle range required for restart when a restart is requested.FIG. 13 illustrates the associated processing sequence. If the actualoperating angle is corrected when a start request is generated, theactual operating angle changes along a straight line passing throughpoint A in FIG. 13 during a process during which the engine temperaturelowers after an internal combustion engine stop.

If, in the above instance, the temperature t1 prevailing at the time ofrestart request generation is known in addition to the stop stateoperating angle A and stop state temperature t0, the actual operatingangle B prevailing at the time of the restart request generation can bedetermined. If the prevailing actual operating angle B is determined,the correction value ΔVL for confining the actual operating angle Bwithin the operating angle range required for restart can be calculated.Therefore, excellent startability can be obtained even if the processfor calculating the correction value ΔVL is repeated during an internalcombustion engine stop, and only the control shaft 12 is adjusted toimplement the correction value ΔVL prior to the start of cranking at thetime of restart request generation.

If the time required for calculating the correction value ΔVL does notsignificantly affect the responsiveness at startup, the crankingsequence may be initiated, without performing any process during aninternal combustion engine stop, after sequentially performing theprocess for calculating the correction value ΔVL according to theprevailing temperature t1 and the process for controlling the controlshaft 12 for implementing the correction value ΔVL when an internalcombustion engine restart is requested. Even when the above method isused, it is possible to restart the internal combustion engine at anappropriate actual operating angle and provide the internal combustionengine with excellent startability.

The fourth embodiment, which has been described above, assumes that thevariable valve mechanism is used with an economy-run vehicle engine,hybrid vehicle engine, or other internal combustion engine having anautomatic stop/start function. However, the present invention is notlimited to such use. More specifically, the present invention providesan optimum operating angle and lift amount, which are suitable forstartup, at a prevailing actual engine temperature t1 when internalcombustion engine startup is requested. Therefore, the variable valvemechanism according to the present invention is also instrumental inimproving the startability of common internal combustion engines.

In the fourth embodiment, which has been described above, the first armmember 44 and second arm member 46 correspond to the “adjustmentmechanism” according to the aforementioned ninth aspect of the presentinvention. Further, the water temperature sensor 25 corresponds to the“temperature detection unit” according to the ninth aspect of thepresent invention. Furthermore, the rotation angle sensor 22 correspondsto the “status detection sensor” according to the ninth aspect of thepresent invention. The “stop state characteristic value detection unit”and “stop state temperature acquisition unit” according to the ninthaspect of the present invention are implemented when the ECU 24 detectsthe actual operating angle A and engine temperature t0 in step 120. The“stop period temperature acquisition unit” according to the ninth aspectof the present invention is implemented when the ECU 24 detects the stopperiod temperature t1 in step 128. The “stop period correction unit”according to the ninth aspect of the present invention is implementedwhen the ECU 24 performs processing step 138.

In the fourth embodiment, which has been described above, the “firstcharacteristic value change amount calculation unit” according to thetenth aspect of the present invention is implemented when the ECU 24performs processing steps 130 and 132 immediately after an internalcombustion engine stop. The “first actual characteristic valuecalculation unit” according to the tenth aspect of the present inventionis implemented when the ECU 24 calculates A+ΔA in step 134 immediatelyafter an internal combustion engine stop. The “suitability judgmentunit” according to the tenth aspect of the present invention isimplemented when the ECU 24 performs step 134 to judge whether thecondition (α≦A+ΔA≦β) is met. The “control shaft correction unit”according to the tenth aspect of the present invention is implementedwhen the ECU 24 drives the control shaft 12 in step 138. The“post-correction characteristic value calculation unit” according to thetenth aspect of the present invention is implemented when the ECU 24performs step 138 to calculate A+ΔA−ΔVL as a new actual operating angleA. The “second characteristic value change amount calculation unit”according to the tenth aspect of the present invention is implementedwhen the ECU 24 performs processing steps 130 and 132 after the controlshaft 12 is corrected. The “second actual characteristic valuecalculation unit” according to the tenth aspect of the present inventionis implemented when the ECU 24 calculates A+ΔA in step 134 after thecontrol shaft 12 is corrected.

In the fourth embodiment, which has been described above, the first armmember 44 and second arm member 46 correspond to the “adjustmentmechanism” according to the aforementioned eleventh aspect of thepresent invention. Further, the water temperature sensor 25 correspondsto the “temperature detection unit” according to the aforementionedeleventh aspect of the present invention. Furthermore, the rotationangle sensor 22 corresponds to the “status detection sensor” accordingto the eleventh aspect of the present invention. The “stop statetemperature acquisition unit” and “stop state characteristic valuedetection unit” according to the eleventh aspect of the presentinvention are implemented when the ECU 24 detects the engine temperaturet0 and actual operating angle A in step 120. The “restart request statetemperature acquisition unit” according to the eleventh aspect of thepresent invention is implemented when the ECU 24 detects the enginetemperature upon restart request generation. The “non-corrective restartrequest state characteristic value calculation unit” according to theeleventh aspect of the present invention is implemented when the ECU 24calculates the actual operating angle A+ΔA (see steps 130 through 134)with the engine temperature prevailing at a restart regarded as t1. The“correction value calculation unit” according to the eleventh aspect ofthe present invention is implemented when the ECU 24 performs processingstep 136. The “pre-restart correction unit” according to the eleventhaspect of the present invention is implemented when the ECU 24 performsprocessing step 138.

1. A variable valve mechanism that is capable of changing the operatingangle and/or lift amount of a valve body of an internal combustionengine, the variable valve mechanism comprising: a control shaft whosestatus is controlled so as to change said operating angle and/or liftamount; a swinging arm that is positioned between a cam and a valve bodyto swing in synchronism with cam rotation, thereby transmitting theforce of the cam to said valve body; an adjustment mechanism forchanging the basic relative angle of said swinging arm in relation tosaid valve body in accordance with the status of said control shaft;temperature detection means for detecting or estimating the ambienttemperature of said control shaft and said cam; and temperaturecorrection means for correcting the status of said control shaft inaccordance with said temperature and in order to avoid the influence ofthe temperature.
 2. The variable valve mechanism according to claim 1,further comprising: a sensor for detecting the status of said controlshaft; an actuator for driving said control shaft; and actuator controlmeans for controlling a control value of said actuator in accordancewith the output of said sensor, wherein said temperature correctionmeans corrects the control value of said actuator in accordance withsaid temperature.
 3. The variable valve mechanism according to claim 2,wherein said temperature correction means corrects the output of saidsensor in accordance with said temperature; and wherein said actuatorcontrol means controls the control value of said actuator in accordancewith the corrected sensor output.
 4. The variable valve mechanismaccording to claim 1, further comprising: a sensor for detecting thestatus of said control shaft; an actuator for driving said controlshaft; target status setup means for setting the target status of saidcontrol shaft; and actuator control means for controlling said actuatorso that the output of said sensor matches the target status of saidcontrol shaft, wherein said temperature correction means corrects thetarget status of said control shaft in accordance with said temperature.5. The variable valve mechanism according to claim 1, wherein saidtemperature correction means comprising: a status detection sensor fordetecting the status of said control shaft; stop state temperatureacquisition means for acquiring said ambient temperature at the time ofan internal combustion engine stop as a stop state temperature; stopstate characteristic value detection means for detecting the operatingangle and/or the lift amount at the time of an internal combustionengine stop as a stop state characteristic value in accordance with thestatus of said control shaft; stop period temperature acquisition meansfor acquiring said ambient temperature during an internal combustionengine stop as a stop period temperature; and stop period correctionmeans for correcting the status of said control shaft during an internalcombustion engine stop so that the operating angle and/or lift amountare maintained suitable for a restart in accordance with said stop statetemperature, said stop state characteristic value, and said stop periodtemperature.
 6. The variable valve mechanism according to claim 5,wherein said stop period correction means including: firstcharacteristic value change amount calculation means for calculating afirst characteristic value change amount in accordance with said stopstate temperature and said stop period temperature; first actualcharacteristic value calculation means for calculating the sum of saidstop state characteristic value and said first characteristic valuechange amount as an actual characteristic value; suitability judgmentmeans for judging whether the calculated actual characteristic value issuitable for a restart; control shaft correction means, which, when theactual characteristic value is judged to be unsuitable for a restart,corrects the status of said control shaft so that the actualcharacteristic value is suitable for a restart; post-correctioncharacteristic value calculation means for calculating a post-correctioncharacteristic value that is obtained by correcting said control shaft;second characteristic value change amount calculation means forcalculating a second characteristic value change amount in accordancewith a change in said stop period temperature that is caused after saidcontrol shaft is corrected; and second actual characteristic valuecalculation means for calculating the sum of said post-correctioncharacteristic value and said second characteristic value change amountas an actual characteristic value.
 7. The variable valve mechanismaccording to claim 5, wherein said internal combustion engine is capableof automatically stopping and starting without requiring an operatorintervention.
 8. The variable valve mechanism according to claim 1,wherein said temperature correction means comprising: a status detectionsensor for detecting the status of said control shaft; stop statetemperature acquisition means for acquiring said ambient temperature atthe time of an internal combustion engine stop as a stop statetemperature; stop state characteristic value detection means fordetecting the operating angle and/or the lift amount at the time of aninternal combustion engine stop as a stop state characteristic value inaccordance with the status of said control shaft; restart request statetemperature acquisition means for acquiring said ambient temperatureupon a request for an internal combustion engine restart as a restartrequest state temperature; non-corrective restart request statecharacteristic value calculation means for calculating a non-correctiverestart request state characteristic value in accordance with said stopstate characteristic value and the difference between said restartrequest state temperature and said stop state temperature; correctionvalue calculation means for calculating a correction value forconverting said non-corrective restart request state characteristicvalue into a characteristic value suitable for a restart; andpre-restart correction means for correcting the status of said controlshaft prior to an internal combustion engine restart so that theoperating angle and/or lift amount change in accordance with saidcorrection value.
 9. A variable valve mechanism that is capable ofchanging the operating angle and/or lift amount of a valve body of aninternal combustion engine, the variable valve mechanism comprising: acontrol shaft whose status is controlled so as to change said operatingangle and/or lift amount; an swinging arm that is positioned between acam and a valve body to oscillate in synchronism with cam rotation,thereby transmitting the force of the cam to said valve body; and anadjustment mechanism for changing the basic relative angle of saidswinging arm in relation to said valve body in accordance with thestatus of said control shaft, wherein a member for determining thedistance between said control shaft and a camshaft and a memberpositioned between said control shaft and said cam are made of materialshaving the same linear expansion coefficient.
 10. The variable valvemechanism according to claim 1, wherein said temperature correctionmeans comprising: a status detection sensor for detecting the status ofsaid control shaft; stop state temperature acquisition means foracquiring said ambient temperature at the time of an internal combustionengine stop as a stop state temperature; stop state characteristic valuedetection means for detecting the operating angle and/or the lift amountat the time of an internal combustion engine stop as a stop statecharacteristic value in accordance with the status of said controlshaft; non-corrective restart state characteristic value calculationmeans for calculating a non-corrective restart state characteristicvalue in accordance with said stop state characteristic value and thedifference between an assumed restart temperature of the internalcombustion engine and said stop state temperature; correction valuecalculation means for calculating a correction value for converting saidnon-corrective restart state characteristic value into an operatingangle and/or lift amount suitable for said assumed restart temperature;and pre-startup correction means for correcting the status of saidcontrol shaft prior to an internal combustion engine restart so that theoperating angle and/or lift amount change in accordance with saidcorrection value.
 11. The variable valve mechanism according to claim10, wherein said pre-startup correction means corrects the status ofsaid control shaft at time of an internal combustion engine stop so thatthe operating angle and/or lift amount change in accordance with saidcorrection value.
 12. The variable valve mechanism according to claim10, wherein said assumed restart temperature is the lowest temperaturewithin an operating temperature range of the internal combustion engine.13. A variable valve mechanism that is capable of changing the operatingangle and/or lift amount of a valve body of an internal combustionengine, the variable valve mechanism comprising: a control shaft whosestatus is controlled so as to change said operating angle and/or liftamount; a swinging arm that is positioned between a cam and a valve bodyto swing in synchronism with cam rotation, thereby transmitting theforce of the cam to said valve body; an adjustment mechanism forchanging the basic relative angle of said swinging arm in relation tosaid valve body in accordance with the status of said control shaft;temperature detection unit for detecting or estimating the ambienttemperature of said control shaft and said cam; and temperaturecorrection unit for correcting the status of said control shaft inaccordance with said temperature and in order to avoid the influence ofthe temperature.
 14. The variable valve mechanism according to claim 13,further comprising: a sensor for detecting the status of said controlshaft; an actuator for driving said control shaft; and actuator controlunit for controlling a control value of said actuator in accordance withthe output of said sensor, wherein said temperature correction unitcorrects the control value of said actuator in accordance with saidtemperature.
 15. The variable valve mechanism according to claim 14,wherein said temperature correction unit corrects the output of saidsensor in accordance with said temperature; and wherein said actuatorcontrol unit controls the control value of said actuator in accordancewith the corrected sensor output.
 16. The variable valve mechanismaccording to claim 13, further comprising: a sensor for detecting thestatus of said control shaft; an actuator for driving said controlshaft; target status setup unit for setting the target status of saidcontrol shaft; and actuator control unit for controlling said actuatorso that the output of said sensor matches the target status of saidcontrol shaft, wherein said temperature correction unit corrects thetarget status of said control shaft in accordance with said temperature.17. The variable valve mechanism according to claim 13, wherein saidtemperature correction unit comprising: a status detection sensor fordetecting the status of said control shaft; stop state temperatureacquisition unit for acquiring said ambient temperature at the time ofan internal combustion engine stop as a stop state temperature; stopstate characteristic value detection unit for detecting the operatingangle and/or the lift amount at the time of an internal combustionengine stop as a stop state characteristic value in accordance with thestatus of said control shaft; non-corrective restart statecharacteristic value calculation unit for calculating a non-correctiverestart state characteristic value in accordance with said stop statecharacteristic value and the difference between an assumed restarttemperature of the internal combustion engine and said stop statetemperature; correction value calculation unit for calculating acorrection value for converting said non-corrective restart statecharacteristic value into an operating angle and/or lift amount suitablefor said assumed restart temperature; and pre-startup correction unitfor correcting the status of said control shaft prior to an internalcombustion engine restart so that the operating angle and/or lift amountchange in accordance with said correction value.
 18. The variable valvemechanism according to claim 17, wherein said pre-startup correctionunit corrects the status of said control shaft at time of an internalcombustion engine stop so that the operating angle and/or lift amountchange in accordance with said correction value.
 19. The variable valvemechanism according to claim 13, wherein said temperature correctionunit comprising: a status detection sensor for detecting the status ofsaid control shaft; stop state temperature acquisition unit foracquiring said ambient temperature at the time of an internal combustionengine stop as a stop state temperature; stop state characteristic valuedetection unit for detecting the operating angle and/or the lift amountat the time of an internal combustion engine stop as a stop statecharacteristic value in accordance with the status of said controlshaft; stop period temperature acquisition unit for acquiring saidambient temperature during an internal combustion engine stop as a stopperiod temperature; and stop period correction unit for correcting thestatus of said control shaft during an internal combustion engine stopso that the operating angle and/or lift amount are maintained suitablefor a restart in accordance with said stop state temperature, said stopstate characteristic value, and said stop period temperature.
 20. Thevariable valve mechanism according to claim 19, wherein said stop periodcorrection unit including: first characteristic value change amountcalculation unit for calculating a first characteristic value changeamount in accordance with said stop state temperature and said stopperiod temperature; first actual characteristic value calculation unitfor calculating the sum of said stop state characteristic value and saidfirst characteristic value change amount as an actual characteristicvalue; suitability judgment unit for judging whether the calculatedactual characteristic value is suitable for a restart; control shaftcorrection unit, which, when the actual characteristic value is judgedto be unsuitable for a restart, corrects the status of said controlshaft so that the actual characteristic value is suitable for a restart;post-correction characteristic value calculation unit for calculating apost-correction characteristic value that is obtained by correcting saidcontrol shaft; second characteristic value change amount calculationunit for calculating a second characteristic value change amount inaccordance with a change in said stop period temperature that is causedafter said control shaft is corrected; and second actual characteristicvalue calculation unit for calculating the sum of said post-correctioncharacteristic value and said second characteristic value change amountas an actual characteristic value.
 21. The variable valve mechanismaccording to claim 13, wherein said temperature correction unitcomprising: a status detection sensor for detecting the status of saidcontrol shaft; stop state temperature acquisition unit for acquiringsaid ambient temperature at the time of an internal combustion enginestop as a stop state temperature; stop state characteristic valuedetection unit for detecting the operating angle and/or the lift amountat the time of an internal combustion engine stop as a stop statecharacteristic value in accordance with the status of said controlshaft; restart request state temperature acquisition unit for acquiringsaid ambient temperature upon a request for an internal combustionengine restart as a restart request state temperature; non-correctiverestart request state characteristic value calculation unit forcalculating a non-corrective restart request state characteristic valuein accordance with said stop state characteristic value and thedifference between said restart request state temperature and said stopstate temperature; correction value calculation unit for calculating acorrection value for converting said non-corrective restart requeststate characteristic value into a characteristic value suitable for arestart; and pre-restart correction unit for correcting the status ofsaid control shaft prior to an internal combustion engine restart sothat the operating angle and/or lift amount change in accordance withsaid correction value.